1. Field of the Invention
This invention relates to a process for the preparation of alkylene glycols from the corresponding alkylene oxide in the presence of water and a SALEN-type catalyst. A specific example of the process is in the preparation of ethylene glycol from ethylene oxide.
2. Description of the Prior Art
The production of alkylene glycols from alkylene oxides is known and is practiced commercially. Of particular interest is the production of ethylene glycol from ethylene oxide. The thermal hydration of ethylene oxide in water produces monoethylene glycol (MEG), a major active component in antifreeze. MEG can also be used as a base material in the production of polyester fibers, resins, films and bottles.
Hydration of ethylene oxide can be through catalytic and non-catalytic means. Non-catalytic hydration of ethylene oxide to MEG requires a large excess of water to inhibit the formation of diethylene glycol (DEG) and other higher glycols. Even with a large excess of water the molar selectivity to MEG is only about 90%. In addition, the water must be distilled from the glycol to obtain a high purity product.
Catalytic hydration of ethylene oxide may use smaller amounts of water and is carried out at lower temperatures. There are numerous examples of catalysts for hydration of an alkylene oxide to alkylene glycol.
N,N′-bis(salicylidene)ethylenediamino(SALEN)-type compounds are known. A metal may be associated with the SALEN-type compound to form a metallosalenate.
U.S. Pat. No. 5,665,890 discloses a process for producing a stereoselectively or regioselectively enriched product by reacting a nucleophile and a chiral or prochiral cyclic substrate in the presence of a non-racemic chiral catalyst. Examples of nucleophiles are amines, mercaptans and alcohols. Epoxides, aziridines, episulfides and certain other cyclic compounds are examples of the substrate. The catalyst may be a metallosalenate catalyst. One reaction disclosed is the asymmetric ring-opening of symmetrical epoxides to resolve a racemic mixture. Hydrolytic kinetic resolution of racemic mixtures having terminal epoxide groups is disclosed in U.S. Pat. No. 6,448,414.
U.S. Pat. No. 5,902,835 discloses a method of preparing polyurethane foam by reacting an organic polyisocyanate with a polyol in the presence of water and a combination of a gelling catalyst and a blowing catalyst. The blowing catalyst may be titanium isopropoxy-SALEN.
U.S. Pat. No. 6,440,745 discloses a method for the combinatorial synthesis, screening and characterization of supported and unsupported organometallic compounds as catalysts, additives and therapeutic agents. SALEN compounds were included as a base scaffold to prepare ligand libraries.